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J. ELLIOT, Jr., & T. A. CUNNINGHAM. STEAM BOILER.

No. 323,647. Patented Aug. 4, 1885.

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(No Model.) 3 Sheet s--Sheet 2.

J. ELLIOT, Jr., & T A. CUNNINGHAM. STEAM BOILER No. 323,647. Patented Aug 4, 1885.

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JJ. ELLIOT, Jr., & T. A. OUNNINGIffiM.

STEAM BOILER- NO. 323,647. Patented Aug. 4, 1885.

LE {1 i Q w t UNITED STATES PATENT FFiCE.

JOHX ELLlOl, JR, AND THOMAS A. CUNNINGHAM, OF DALBEATTIE, COUNTY OF KIRKCUDBRIGHT. SCOTLAND.

STEAM-BOILER.

SPECIFICATION forming part of Letters Patent No. 323.6417, dated August 4, 1885. A pplicution filed December 18, 1884. (No model.) Patented in England May 28, 1883, No. 2,643.

To all 1071 0722 it may concern.-

Be it known that we, JOHN ELLIOT, Jr., and THOMAS ALLIsoN CUNNINGHAM, subjects of the Queen of Great Britain and Ireland, and residing at Dalbeattie, in. the county of Kirkcudbright, Scotland, have invented certain Improvements in and Connected with Steam- Boiler and other Furnaces, (for which We have obtained a British Patentdated May 28, 1883, No. 2,643,) of which the following is a specification.

Our said invention has for its object to economize fuel in steamboiler and other furnaces; and it consists, principally, in an apparatus for supplying the air required for the combustion of the fuel in a compressed and heated state, and in such a manner as to cause a vigorous circulation of the fire-gases by making a portion of them pass again over, through, or in contact with the burning fuel.

Our invention is applicable to various kinds of steam-boilers and furnaces. On the accompanying three sheets of explanatory drawings we have shown our apparatus as applied to marine boilers of an ordinary type. These boilers, which are shown in sectional front elevation in Figure 1, in vertical section in Fig. 2, and in plan in Fig. 3, have internal furnaces, 3, atboth ends, with a combustionchamber, 4, at the middle, and with tubes above the furnaces, through which tubes the fire-gases return from the inner ends to smokeboxes 6 at the outer ends. There are two furnaces and two smoke-box doors, 7, at each end of each boiler, some of these doors being supposed to be removed in Fig. 1. Above each furnace there is placed in the smoke-box 6 a vertical return-pipe, S, the upper end of each pipe being just above the lowermost tubes, 5, and being formed with an open flared or funnellikc mouth, 9, while the bottom end commu- 111' catcs with the interior of the furnace. A small pipe, 10, is arranged to extend from above down toward and nearly into each return-pipe S, and a jet of compressed and heated air is forced in through this small pipe 10, and, issuing through a small hole in a nozzle or thimbie, 11, at the lower end, has the effect of drawing in and forcing down the larger pipe 5o 8 a portion of the firegases which have passed through the tubes 5 and are (in existing boilers) on their way to the chimney or uptakefunnel 12. The air introduced by the small pipe 10 is compressed-and forced in by means of a pump,and becomes heated in consequence of its compression. It may also be additionally heated by being passed through pipes 13 in the uptake 12, or through casings or regenerative chambers heated by the fire-gases prior to. the ultimate escape or discharge of these gases by the chimney or uptakefunnel.

The action of the air-jet causes the firegases to pass more rapidly through the tubes 5, which renders them more effective in generating steam,and at the same time keeps the 6 tubes cleaner, and, complete ignition of any combustible portions of the gases or of suspended carbonaceous particles which may escape combustion when first passing through the tubes is insured by the air-jet, added to 7Q which an increased heat is maintained in the furnace. By these means a great economy of fuel is effected, and steam-boilers for a given power may be considerably reduced in size.

The return-pipes 8, through which the firegases are made to return to the furnaces,may be constructed to pass through the water of the boiler, so as to be available as additional heating-surface. The ordinary inlets for air into the furnace above the grate are closed,and the air forced in with the fire-gases is led into the furnace either by one inlet or by two or more branches in each case. Thus some of the mixed air and gases may be led in above the grate and some below it; and, if found desirable, some may be led by a branch pipe to the bridge or inner end of the furnace. Vhen led in below the grate, the ash-pit may be closed.

The quantity of air supplied may be varied, when desirable, by altering the speed of the pump or apparatus, by means of which it is forced through the small pipes 10; or air may be forced uniformly through those pipes, and additional supplies may, if required, be drawn 9 5 or driven in by the action of jets. For this purpose there is connected to each large return-pipe 8 a branch from an air-pipe, 14, having an inlet-mouth, 15; and a branch j et-pipe,

16, from the compressedair pipe 10, directs a zoo jet of air into this mouth, so as to cause additional air to enter by the pipe 14 and mix with the descending fire-gases in the returnpipes 8.

5 In some kinds of furnaces the return-passage for a portion of the gases may be a flue formed in or lined with brick, the air-jet be ing applied so as to propel the gases along such return-passage.

10 What we claim as our invention is 1. The combination of the fire-place and fluetubes 5 of a steam-boiler with a return-pipe, 8, leading from the smoke-box behind the tubes back to the fire, and a compressed-air 1 pipe, 10, opening into the return-pipe to return a portion of the fire-gases after they have passed through the tubes 5 back again into contact with the fuel, substantially as set forth. 2. The combination of the fire-place and fine 20 tubes of a steam-boiler with a return-pipe, 8, leading from the smoke-box behind the tubes to the fire, a compressed-air pipe, 10, opening into the said return-pipe,the said compressedair pipe having portions 13, passing through the heating-space in the furnace, substantially 25 as described.

3. The combination of the fire-place and fluetubes of a steam-boiler with a return-pipe, 8, leading from the smoke-box behind the tubes to the fire, and compressed-air pipe 10, open- 0 

